Diagnostic apparatus with an automatic visualization of scan planes

ABSTRACT

A diagnostic apparatus ( 1 ) according to the invention is arranged to comprise imaging means ( 6 ) for acquiring diagnostic information within a volume of a patient (P) being located with an imaging volume ( 1 ′) of the diagnostic apparatus ( 1 ). In order to visualise the spatial position and orientation of an actual scanning plane on the skin of the patient corresponding to an actual diagnostic image, the diagnostic apparatus ( 1 ) comprises visualisation means ( 10,11,12 ). The visualisation means ( 10,11,12 ) are arranged in an immediate vicinity of the imaging volume ( 1 ′) and can be realised as a set of light fan beams. The correct position of the light fans with respect to the actual imaging plane can be mechanically adjusted or can be adjusted by means of a mirror-based optical arrangement.

The invention relates to a diagnostic apparatus comprising an imagingvolume for accommodating a patient to be imaged, means for positioningthe patient within the imaging volume, imaging means arranged to acquirea diagnostic image in an imaging plane of the patient positioned in theimaging volume.

The invention further relates to a method for guiding an interventionalapparatus using the diagnostic apparatus.

An apparatus to perform diagnostic studies by means of a spin magneticresonance of a patient located in the imaging volume of said apparatusis known from U.S. Pat. No. 6,275,721. The known apparatus is furtherequipped with a visual feedback to provide an information about asighting axis towards the imaging plane. This information is provided bya visualization of an impingement point of said axis on the patient'sskin by means of a visible laser diode.

The known apparatus has a disadvantage that no information about theorientation of the scan plane is provided for analysis by the operator.In order to find the entry lines of the scan plane on the surface of thepatient the operator has to reconstruct the spatial orientation of theactual plane. This is a very difficult and unreliable procedure as it isbased upon the diagnostic image comprising a target area. For obliquescan planes this may lead to a very inaccurate result. Thus, providedwith only a given projection of the sighting axis on the surface of thepatient it is not feasible for the operator to deduct the entry lines ofthe actual scan plane, which is particularly important for conductinginterventional procedures.

It is an object of the invention to provide an improved diagnosticapparatus.

The diagnostic apparatus according to the invention is characterized inthat the diagnostic apparatus further comprises visualization meansarranged to visualize a spatial position of the imaging planes withinthe imaging volume. According to the technical measure of the inventionthe operator is provided with a tangible information about theprojection of the scanning plane onto the patient. This information canbe used during a therapy planning procedure, where the exact location ofthe entry lines of the scan plans must be known in order to plan asubsequent radiotherapy. The technical measure of the invention is alsoadvantageous for planning follow-up examinations, where the patient mustbe scanned in exactly the same scanning planes as during a previousexamination. By positioning the patient in such a way in the imagingvolume that the actual scan planes spatially coincide with the markedprevious plane a greater reliability of the follow-up consistency can beguaranteed. Furtheron, the technical measure of the invention can alsobe applied in the field of medical interventions, where an examinationapparatus, or a biopsy needle has to be inserted into the patient with ahigh spatial accuracy. By visualizing the entry lines of the scan planeson the skin of the patient the position of the incision can becontrolled better. Furtheron, this technical measure simplifies theprocedure for bringing markers for representing an internal lesion onthe patient's skin. It must be noted that the technical measure of theinvention can be integrated in a wide variety of medical diagnosticapparatus, for example an X-ray apparatus, an MRI apparatus or acomputer tomograph.

An embodiment of the invention is characterized in that thevisualization means are arranged in the immediate vicinity of theimaging volume and in that the visualization means comprise anadjustable light fan. By providing a plurality of light sources withfan-like bundles a spatial position of a plane can be visualized.Preferably, the light sources are located within a bore of a bore-typeapparatus, or are mounted on a foot- or ceiling based arm for aconventional X-ray apparatus. The correct position of the light fans canbe adjusted mechanically or using mirrors, which are controlled by theunit controlling the orientation of the scan planes. In this way adirect link between the diagnostic information and an external anatomyof the patient is obtained.

A further embodiment of the apparatus according to the invention ischaracterized in that the visualization means further compriseindicators to visualize a selected area within the imaging plane. Anexample of such a selected area can be a center of the plane.Alternatively, the operator can indicate with a cursor an incisionposition on the diagnostic image and the visualizing means can bearranged to visualize the selected incision point of the surface of thepatient. Due to this technical measure the guiding of a medicalinstrument during the interventional procedures can be performed with anincreased reliability.

A method according to the invention is characterized in that said methodcomprising the steps of positioning a patient within the imaging volumeof the diagnostic apparatus; using the imaging means for acquiring adiagnostic image in a plane comprising a target area of the patient;using the visualization means for visualizing a projection of theimaging plane of said diagnostic image on the patient's skin. Byapplying the method according to the invention the operator is providedwith an accurate information about the spatial relation of the plane ofthe diagnostic image comprising a target area, for instance a lesion andthe external anatomy of the patient. In this way a direct link isprovided between the location of internal anatomy, target areas and theexternal world. This information is of particular importance forinterventional applications.

A further method according to the invention is characterized in thatsaid method comprises the steps of: positioning a patient within theimaging volume of the diagnostic apparatus; using the imaging means foracquiring a diagnostic image in a plane comprising a target area of thepatient; calculating an approach trajectory for the interventionalapparatus, said trajectory comprising an entry point on the patient'sskin and a target point within the target area; visualizing the entrypoint together with a projection of the imaging plane of the diagnosticimage on the patient's skin. The method according to the invention isparticular valuable for guiding the interventional procedures. It iswell known, that for some applications, for example for cranialinterventions, it is of vital importance not to damage certain areas ofa healthy tissue. By applying the method according to the invention theoperator can select a target area on the acquired diagnostic image, andthe system can provide the optimal approach trajectory including anentry point on the skin surface of the patient and the selected pointwithin the target area. When the optimal trajectory is calculated, thelocation of the entry point can be visualized on the skin of the patienttogether with the projection of the plane of the diagnostic image. It isalso possible to add an additional visual guide to simplify thedetermination of the angular orientation of the interventional apparatuswith respect to the entry point.

These and other aspect of the invention will be discussed in more detailwith reference to figures.

FIG. 1 presents a schematic view of an embodiment of the diagnosticapparatus according to the invention.

FIG. 2 shows schematically a first embodiment of the visualization meansaccording to the invention.

FIG. 3 shows schematically a second embodiment of the visualizationmeans according to the invention.

FIG. 4 shows schematically an embodiment of the diagnostic apparatusarranged to carry out the method according to the invention.

FIG. 1 shows schematically an embodiment of the diagnostic apparatusaccording to the invention. In this figure the diagnostic apparatus 1 isa conventional bore-type magnetic resonance apparatus comprising asupport table 2 which is movable to arrange a patient P to be examinedan imaging volume 1′ of the diagnostic apparatus 1. The operationalprinciple of such an apparatus is known, for example from WO 98/10303and lies within the scope of knowledge of the person skilled in the art.A central control unit 5 of the MR-apparatus 1 is arranged to controlgradient coils (not shown) by sending an appropriate signal to arespective coil control system 3 defining each component Gx, Gy and Gzof the gradient field. The imaging means 6 are arranged to acquire adiagnostic image from the imaging plane defined by the gradient field.The spatial position and orientation of the imaging plane isunambiguously defined when all three components Ox, Gy and Gz of thegradient field are defined. Therefore, by using this information it ispossible to unambiguously define a visual plane representing the imagingplane of the diagnostic image in the imaging volume. This is carried outin the diagnostic apparatus according to the invention by means of acontrol unit 9 which is controlled by the central control unit 5 incoherence with the control unit 3 of the gradient coils. The actualvisualization of the imaging plane is performed by means of light fans10′, 11′, 12′ propagating in the imaging volume 1′ from thelight-emitting diodes 10, 11, 12 arranged in the bore of the diagnosticapparatus 1. A line L representing an intersection of a light fan withthe surface of the patient represents the projection of the imagingplane on the patient's skin. The operator is thus provided with thevisualization of the spatial position of the imaging plane together withthe diagnostic data presented on the console 7. The visualization meanscan be realized for example by light sources emitting light fans, thecorrect position of the fans with respect to the imaging plane beingmechanically adjusted or being adjusted by means of a mirror-basedoptical arrangement.

FIG. 2 shows schematically a first embodiment of the visualization meansaccording to the invention. The visualization means 20 l, 20 r can bearranged in an immediate vicinity of the patient table 2, preferably inthe imaging volume (not shown in FIG. 2). Alternatively, thevisualization means 20 r, 201 can be arranged in the bore of thediagnostic apparatus. This can easily be implemented especially forso-called open MR-scanners. The embodiment shown in FIG. 2 comprises anassembly of a two floor-mounted arms, each arm bearing a light fansource 22 l, 22 r, respectively, emitting visible light in a fangeometry, indicated by 24 l, 24 r. In general, the systemsconventionally suited for the patient positioning and alignment are wellsuited to be used as visualization means within the teaching of thepresent invention. In order to visualize an oblique plane, each arm isrotatable around three orthogonal axis, as schematically is indicated byarrows 30, 31, 32 in FIG. 2. The rotation of the arm is controlled by aconventional drive (not shown) in accordance with a signal from thecontrol unit 9 (see FIG. 1). The visualization means 20 l and 20 r canbe further equipped with indicators 27 l, 27 r in order to visualize aselected area on the surface of the patient P. This can be realized incase the indicators 27 l and 27 r emit visible light in a substantiallypencil-bean geometry, as is schematically indicated by 27′l, 27′r. Theposition of the corresponding light spot from the beams emitted by theindicators 27 l, 27 r can be adjusted by means of a mechanical drive ofthe indicators 27 l. 27 r or, alternatively can be optically adjusted bymeans of mirrors. According to this technical measure the position ofthe resulting light spot on the patient's surface can be shifted incompliance with the position of the selected area.

Alternatively, it is possible to use a stationary post-based matrix ofpencil light-beams, where the orientation of the resulting fan will begiven by a selective energizing of a set of light elements in the matrixin accordance with the spatial position of the scanning plane. Anexample of such an arrangement is given in FIG. 3 (for simplicity onlyone unit is being shown). As is shown in FIG. 3, the visualization means20 comprise a matrix of light emitting elements 26. The visualizationmeans 20 are arranged in an immediate vicinity of the patient supporttable 2. In order to represent the actual imaging plane, a set of thelight-emitting elements 26 are energized as is schematically indicatedby squares 28 in FIG. 3. The spatial and angular resolution of such asystem depends upon the total number of the light-emitting elements inthe matrix 20. By appropriately choosing the total number of thelight-emitting elements a simple yet reliable device can be produced.

In order to match the position of the resulting light beam with theposition of the imaging plane in the longitudinal direction, the arm orthe matrix can be translatably arranged in the longitudinal direction.

FIG. 4 shows schematically an embodiment of the diagnostic apparatusarranged to carry out the method according to the invention. Thediagnostic apparatus 1 is a conventional bore-type magnetic resonanceapparatus comprising a patient support 2 to position the patient Pwithin the imaging volume 1′ of the diagnostic apparatus 1. Inaccordance with FIG. 1, the imaging plane of the diagnostic apparatus isdefined by a set of gradient fields Gx, Gy, Gz defined by the centralcontrol unit 5 and controlled by the control unit 3 of the gradientcoils. The control unit 9 of the visualization means 10, 11, 12 iscontrolled by the central control unit 5 in accordance with the signalssent to the control unit 3 of the gradient coils. The imaging means 6are arranged to acquire a diagnostic image from the imaging planedefined by the gradient field. The acquired resonance signals from theexcited imaging plane are reconstructed using an appropriatereconstruction soft-ware and are graphically represented on the console7 for the analysis of the operator. At the same time the correspondingimaging plane is being visualized on the surface of the patient P bymeans of the light fans 10′, 11′, 12′ emitted by the visualization means10,11,12. A line L representing an intersection of the light fans withthe patient's surface unambiguously indicates the spatial position ofthe actual scanning plane on the patient's surface. In case the patientP is undergoing an interventional procedure it is of a great importancethat the interventional apparatus (needle or a medical device) is beingintroduced into the patient with as little damage to healthy tissue aspossible. The accurate selection of the entry point of theinterventional apparatus on the patient's skin is ensured due to thefact that the projection of the actual imaging plane comprising a targetarea is being visualized on the surface of the patient by means of theprojection line L. By using the anatomical information contained in thediagnostic image the operator can deduce the correct position of theentry point on the external surface of the patient. By performing anon-line image acquisition during the insertion of the interventionalapparatus, the manoeuvering of the latter in an accurate and correct wayis ensured.

Alternatively, in case critical tissues are adjacent to the area of amedical intervention, the accurate positioning of the interventionalapparatus within the patient can be controlled using a second embodimentof the method of the invention. According to the second embodiment ofthe method of the invention the operator selects the imaging planecomprising a target area. Then, the operator can interactively define atarget point on the target area of the patient. The diagnostic apparatuswill then calculate a shortest approach trajectory comprising the targetpoint and an entry point on the surface of the patient, said approachtrajectory being preferably a straight line avoiding critical tissues.Such a calculation is performed in the diagnostic apparatus 1 by meansof a dedicated computer program stored in the system computer 8. Anexample of such a computer program is a decision support system (DSS)known in the art of medical application, the program comprising forexample tabulated tissue data and corresponding weighing coefficientsrepresenting the clinical crucially of the organs. The optimaltrajectory is then calculated based on the optimization of the totalvalue function representing a cost function. Optimization methods of thekind are known in the field of combinatorial optimization. After theoptimal approach trajectory is calculated, an appropriate signal is sentto the control unit 9 of the visualization means. In case thevisualization means, as schematically presented in FIG. 2, are furtherequipped with an indicator to indicate a selected area on the surface ofthe patient, said area I being visualized for the operator in accordancewith the calculated entry point for the interventional apparatus. Theoperator is thus provided with an accurate position of the incisionpoint, which is of a great importance especially if the imaging plane isobliquely oriented with respect to the patient. By performing an on-lineacquisition of the imaging data during an interventional procedure, theoperator can be ensured that the manoeuvering of the interventionalapparatus takes place in accordance with the calculated optimal approachtrajectory. This technical measure ensures a safe an accurate conduct ofthe interventional procedures.

While this invention has been described with reference to particularembodiments and examples, other modifications and variations will occurto those skilled in the art in view of the above teaching. Accordingly,it should be understood that within the scope of the appended claims theinvention may be practiced otherwise than is specifically described.

1. A diagnostic apparatus comprising an imaging volume for accommodatinga patient to be imaged, means for positioning the patient within theimaging volume, imaging means arranged to acquire a diagnostic image inan imaging plane of the patient positioned in the imaging volume,characterized in that the diagnostic apparatus further comprisesvisualization means arranged to visualize a spatial position of theimaging plane within the imaging volume.
 2. An apparatus according toclaim 1, characterized in that the visualization means are arranged inthe immediate vicinity of the imaging volume and in that thevisualization means comprise an adjustable light fan.
 3. An apparatusaccording to claim 2, characterized in that the visualization meansfurther comprise indicators to visualize a selected area within theimaging plane.
 4. A method for guiding an interventional apparatus usinga diagnostic apparatus according to claim 1, said method comprising thesteps of positioning a patient within the imaging volume of thediagnostic apparatus; using the imaging means for acquiring a diagnosticimage in an imaging plane comprising a target area of the patient; usingthe visualization means for visualizing a projection of the imagingplane of said diagnostic image on the patient's skin.
 5. A methodaccording to claim 4 characterized in that said method further comprisesthe step of inserting the interventional apparatus in the patientaccording to the information contained in the diagnostic image and theimaging plane visualization on the patient's skin.
 6. A method forguiding an interventional apparatus using a diagnostic apparatusaccording to claim 1, said method comprising the steps of: positioning apatient within the imaging volume of the diagnostic apparatus; using theimaging means for acquiring a diagnostic image in a plane comprising atarget area of the patient; calculating an approach trajectory for theinterventional apparatus, said trajectory comprising an entry point onthe patient's skin and a target point within the target area; andvisualizing the entry point together with a projection of the imagingplane (L) of the diagnostic image on the patient's skin.
 7. A methodaccording to claim 6, characterized in that said method furthercomprises the step of inserting the interventional apparatus in thepatient according to the calculated approach trajectory, the entry pointand the imaging plane visualization on the patient's skin.